Cost Effective and Timely Purging Using MOP Oxygen Meter

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Vessels filled with air have to be purged with carbon dioxide to remove oxygen.  The goal is a purge strategy to get the oxygen below 1%  while using the minimal amount of expensive carbon dioxide in the shortest possible time.  A higher CO2 flow rate does not necessarily mean a shorter purge time if introduced to the tank incorrectly.

TAKE ADVANTAGE OF THE HIGHER DENSITY– Carbon dioxide with a molecular weight of 44 is heavier than air with a molecular weight of 29.  This  difference can be used during the purge cycle.  Carbon dioxide is initially introduced to the tank at a lower flow rate through a device that directs the flow to the bottom of the tank that minimize turbulence.  As more carbon dioxide gas is added and when the volume delivered results in an interface level above the introduction port, the carbon dioxide flow rate is increased greatly which acts as a piston below the air forcing it out of the vent line.

AVOID TURBULANCE – Carbon dioxide flow into the tank has to be controlled to minimize turbulence.  Turbulence of one gas flowing through the other will mix result in an extend purge time.  

MONITOR INLET FLOW AND O2 CONCENTRATION –The Minimized Oxygen Purge (MOP) meter and the Impact MF carbon dioxide flow meter with needle valve are used together to control the flow rate of CO2 into the tank and monitor the oxygen concentration at the purge outlet.   The goal in purging is to approach the theoretical minimum volume of carbon dioxide gas which is the physical volume of the tank.  The oxygen concentration curve should be as close to vertical as possible.   This indicates the CO2 is acting like a piston, displacing the air.  The more flat the line, the more mixing is indicated and more CO2 gas is required to purge the tank.

MOP TO MINIMIZE PURGE TIME AND CO2 CONSUMPTION – The goal of using the totalizing flowmeter and gas oxygen concentration meter together is to provide tools to minimize carbon dioxide gas usage and minimize the time required to purge the tank to less than 1% oxygen by volume.

STOP USING THE SMELL TEST - The traditional method of detecting when oxygen has been purged from a line is using the smell test. Pure carbon dioxide is very harsh on the mucus membranes as carbonic acid forms when combining with water.  This is a dangerous practice and is not a very accurate measurement of residual oxygen.   MOP provides a safe, high accuracy oxygen concentration measurement in a brewery.